In the field of automobiles, for instance, controlling the quality of the manufactured part is particularly important, specifically for guaranteeing the quality/compliance of parts. Generally speaking, the production of parts at least partially made of filled elastomer must comply with particular specifications. Such specifications define characteristics that the part must comply with, such as the measurement of stiffness and of the phase so as to determine the loss angle for one or more mechanical stress(es).
The characteristics to be determined can be quasi-static characteristics, for instance. For this purpose, methods for determining such characteristics implement quasi-static regime testing, i.e. a stress is gradually applied onto the part to strain it. The quasi-static regime strain rate for the part is frequently of the order of 10 mm/min. Such methods generally use a traction-compression machine. In this type of machine, the part to be analyzed is fixed to a testing bench of the traction-compression machine and to a jack thereof, in order to study the behaviour of the part when submitted to an axial, or radial, conical or torsional stress. The jack is translatable, so that it can successively exert a compressive stress and a traction stress onto the part. The part strain (generally measured by the height of the part parallel to the direction of the applied stress) and the load applied are measured during the compression and traction phases in order to obtain a stress/strain transfer curve. Stiffness and damping are then determined from such measurements.
Because the part has to be fixed to elements of the traction-compression machine to apply the successive compressive and traction stresses, such methods require a relatively long time, generally above 10 min for each part measured. They additionally require trained personnel to correctly position the part in the machine and execute the test. Such methods thus cannot be implemented in a production line, in order to control the quality of all the parts which are manufactured for rate reasons, taking off samples being required to fix same to the traction-compression machine.
Additionally, the specifications also sometimes require checking the compliance with mechanical characteristics in dynamic mode for one or several strain(s) and one or more frequency(ies). Such measurements are conventionally made using servo-hydraulic traction-compression machines. Constraints are applied onto the part so that the strain curve of a control area of the part describes a sinusoid. The sinusoid frequency is preferably greater than or equal to 1 Hz. Fixing the part is thus all the more necessary since it must keep up with such strain frequency.
Servo-hydraulic traction-compression machines are rather expensive, too.
For information for the person having ordered the parts, or the final user, such dynamic characteristics sometimes have to be obtained for several frequencies and maximum strain. The steps mentioned above are thus repeated for several strains and several frequencies of application of different stresses.
Besides, all these methods consume larger amounts of energy, whether in terms of oil, electricity or water consumption. They also require trained operators and are noisy. The global cost of such measures is thus relatively high.
The document WO 2012/080675 relates to a method of driving in a quasi-static and modulated manner a test device for trials of mechanical loadings on a sample produced essentially from one or more materials exhibiting visco-elastoplastic behaviours, allowing the characterisation of the mechanical behaviour of the sample and the modeling of this behaviour. Such device comprises at least one mechanical loading assembly comprising at least one actuator making it possible to move a gripping means in axial displacement, along the axis of the sample held in the loading position. It consists essentially, on the basis of a computer, in controlling the or each actuator by sending and by injecting into the latter a signal representative of a speed setting or force setting, said signal being a sinusoidal modulated signal v(t) comprising a quasi-static component and a sinusoidal dynamic component. The document WO 2012/080675 also relates to a test device suitable for implementing the method.
The state of the art also comprises the document FR 2 925 691 and the articles by COVENEY V A et Al: A triboelastic Model for the Cyclic Mechanical Behaviour of Filled Vulcanizates and Rate-dependent modeling of a highly filled vulcanizate published in RUBBER CHEMISTRY AND TECHNOLOGY, AMERICAN SOCIETY, RUBBER DIVISION, US, respectively volume 68, no 4, Sep. 1, 1995, pages 660-670 and volume 73, no 4, Sep. 1, 2000, pages 565-577.
The need therefore exists for a method for characterizing the mechanical behaviour of parts subjected to stresses which can be directly implemented in a line of production of such parts.